In article . net,
chuck wrote:

You seem to be saying that sea water (which is one heck of a lot less
conductive than copper -- I mean orders of magnitude less conductive) is
the only rf ground (return path) that works? And that the only way to
utilize it in a fiberglass hull is with capacitive coupling?

By your reasoning, radio communication from a vessel on fresh water is
impossible.

Or, as a corollary, radio communication from a vessel on the hard is
impossible because the capacitive coupling to the sea is over a distance
of more than 12".

And of course, for VHF, we all use the equivalent of copper that is not
capacitively coupled to the sea. Since we all agree that VHF works fine
that way, can you tell us at what frequency the laws of electromagnetic
radiation "jump ship" and no longer work the same as at VHF? A reference
would be most welcome. The issue here is radiation, not propagation.

Can you also provide a reference to the published and repeatable testing
of 400 sq. ft. of copper ground that didn't work any better than having
nothing at all? Radio stations thousands of miles from the sea would be
amazed to learn that their ground systems don't work better than nothing
at all.

Why not post your theory on rec.radio.amateur.antenna and see how it is
received there?

Suggest you reef those sails a tad, Me.

Chuck

Well Chuck, now lets look at the subject a bit and see what the
difference is between your VHF analogy, and MF/HF RF Ground systems.

Copper vs Salt Water at VHF....Very significant difference in
conductivity, but it isn't conductivity that we are dealing with here.
At VHF the RF Ground side of the antenna is built into the antenna,
and needs only to be .5 meters long. (roughly) Also consider that at VHF
an antenna can operate over a very wide Frequency Range (155-159 Mhz)
without any major RF Impedance changes. This is NOT even close to being
true at MF/HF frequencies. Move your frequency 250Khz and your antenna
tuning is totally blown away.

Copper vs Salt Water at MF/HF.....Still some what significant in
Conductivity, but again it isn't conductivity we are talking about here.
When was the last time you saw a vessel dragging around a pile of copper
so as to have a Good RF Ground, no matter what the hull was made of?
At MF/HF Frequencies the RF Impedance of the Ground System is inversely
proportional to coupling to the Salt water, if the vessel is floating in
salt water. Obviously you have never tried to communicate using MF/HF
Frequencies in the Great Lakes and Mississippi River Systems from
plastic or wood hulled vessels. It is a bitch to design an effective RF
Ground for such vessels, as there just isn't enough there to make it
work, like in Salt Water. Also remember that RF Impedance changes with
Frequency, a rather LARGE point to be made here. When you are designing
a Marine RF Ground system it must work across one order of magnitude, or
better in frequency span, and provide a Low Impedance across the whole
span. Now tell us all just how you accomplish this feat of magic with
a plastic or cellulose hull sitting in fresh water? Like I said, it is
a bitch, and a compromise in the best situation.

The Laws of Physics aren't the problem here, it is how the Frequency
interacts with RF Ground System Impedance that determine how well things
work. No "Jump ship" about it, just simple Physics, that you apparently
don't have a good handle on.

Radio Stations in the MF Frequency Band use Marconi Antennas, and or
Phased Marconi Antennas, for Transmission. These have EXTENSIVE
RF Ground Systems, usually made up of over 100 1/4 Lambda length radial
wires buried 6 to 10" below the surrounding surface, depending on the
Radiation Pattern for that station, as designated on the License issued
by the FCC. These RF Grounds are engineered specifically for the site
and Radiation Pattern needed. The RF Ground for such Systems covers
significantly more area than 400 Sq Ft, and the addition of such a small
area of copper screen, wouldn't make any significant difference to the
Impedance of such a Ground System. What few HF Stations that are
licensed in the US these days, mostly use Balanced Antennas instead of
Marconi Antennas and the RF Ground isn't nearly as significant to their
operation as it is for Marconi Antennas. The significance is basically
limited to Takeoff Angles. Also of some significance here is that all
these situations are single frequency antennas, and therefor don't need
to be Low Impedance across a wide spread of frequencies (an order of
magnitude or better when opertional. If you had some practical knowledge
in the field, you would notice that if a wet, swampy field, or marshland
could be found, that is where these antenna systems are built. Can you
guess why?

Having been in both the Bradcast Engineering, and Marine Radio
Engineering end of things for MANY years, and having designed, installed,
and maintained both classes of systems, I have dealt with these issues
for MANY years, and the moral to the story IS, " It's the RF Ground,
Sonny, the RF Ground".

Me been there, done that......for a long long time.....